Percussive tool



Sept. 30, 1941` A. T. LUNDGREN TAL 2,257,267

PERCUS S IVE TOOL Filed May 6, 1938 '3 Sheets-Sheet l Sept. 30, 1941. A.T. LUND'GREN ET AL PERCUSSIVE TOOL Filed May 6, 1938 V u v3 Sheets-Sheetf5 Fg. 7

,4a/vf TLU/VDGQEN, Auf/v 5 @oms-Q5 and Patented Sept. 30, 1941PERCUSSIVE TOOL Agne T. Lundgren,

Trollhattan. Alvsborgs Lan. Sweden, and Allan B. Rogers and Vladimirlavlecka. Santa Monica, Douglas Aircraft Company, Inc., Calif., acorporation of Delaware B. Calif., assigner: to Santa'Monica,

Application May 6, 1938, SerialNo. 206,364 y (CLglZl-ZD 11 claims.

This invention relates in general to fluid pressure actuated percussivetools and in particular to single impact riveting hammers particularlyadapted to iiush riveting.

In certain industries, such, for example, as the airplane industry,metal sheets are secured tgether by iiuSh-riveted joints. It is foundthat for many purposes the most suitable hush-riveted joint is thatwherein rivets having heads of the counter-sink type have lsuch headsseated in recesses, herein referred to as dimples, formed by bendinginward the annular metal portions of the overlying sheets surroundingthe openings through which the shank ol the rivet passes. as

distinguished from the ordinary type of countersink which .is formed bycutting away sufficient of the metal of one or more of the sheets toform a recess which will receive part or all of the rivet head.

It is an object of the present invention to provide` simple andeilective means for forming a flush-riveted joint wherein the rivet headis received in a dimple formed by impacting the head of the rivet whilethe assembly of overlying sheets are buck'ed from 'the back in such amanner and with such cooperative buckingv means that the head of therivet thus impacted will deilect the edge portions of the sheetssurrounding the rivet holes inwardly and thereby form a dimple incooperative relation to the rivet head. i

It is a further object of the invention to provide means of simple andeffective character for forming a flush-riveted joint of the type setforth in the preceding paragraphs, which will consistently position theheads of the rivets in co-planar alignment with the-surface of the frontsheet of the assembly of over-lying sheets included in the hush-rivetedjoint.

An important object of this invention is to provide a single-actingriveting hammer which produces an impact greater than heretofore attain-'fluid pressure is surrounding metal, as well as in securing relationwith the dimpled portions of the sheets.

Another object of the invention is to provide a riveting.forward-movement of the hammer piston until a built up behind the pistonapproximately equal to the pressure in the fluid supply line with whichthe device is connected.

Another object is to provide the riveting hammer with a differentiallyoperable pressure transier valve together with means operable bythevalve for restraining and releasing the piston.

Another obiect is to provide the riveting hammer with a manuallyoperable main valve, a Dressure transfer valve that is differentiallyresponsive to operation of the main valve, and means releasablyrestraining the piston at the breech of the cylinder, this releasingmeans operating in Va. timed relationto the transfer valve.

Another object is to provide means for maintaining a pressure in back of the hammer piston A of a riveting hammer at approximately the presmerfrom the front to preparatory to the work 4o pacting the rivet headtogether with a able with a riveting hammer having a piston of the sameweight and diameter,a stroke of the same length, and an air supply atthe same pressure.

Another object is to provide a riveting hammer for use in flush rivetingwhich produces a single impact of sufficient force to impact-dimple aplur'ality of metal sheets into nested relation with the head of arivet.

Another object is to provide a riveting hammer for use in ush rivetingwhich produces a single impact of suiiicient force 'to upset the shankof a rivet into concentrically sealing relation with the sure in the airsupply line during the work stroke of the piston and to provide meansfor reducing to a minimum the back pressure in iront of the piston of ariveting hammer during the work stroke of the piston.

Another object is matically returning the to provide means forautopiston of a riveting hamthe rear of the cylinder stroke of thepiston. Another object is to provide a riveting hammer which operateswith maximum economy for the reason that the loss of air therefrom isminimized.

Another object is to provide a riveting harnmer with a drivinghead whichis adapted to the seating of the rivet-and shank where the sheets beingjoined together are suillciently resilient to permit upsetting. by imyportion of that is also adapted to bucking the rivet and to holding therivet headflush with the surface of the outer sheet in the operationwherein upsetting is accomplished by impacting the shank.

Another object is to provide a riveting ham mer with a driving headhaving means for auto# matic parallel alignment' of the work with thesurface of the outer sheet.

Another object is to provide a riveting hammer with a driving headhaving means for preventing slippage while being held against the work.v

Another object is to provide a riveting hammer with a bucking head whichis adapted to bucking the outer sheet,and

'55, the sheets while the rivet is being seated and hammer having meansfor restraining t to the upsetting of the surface which is adapted tothe upsetting operation where upsetting is accomplishedby impacting theshank.

Another object is to provide a riveting hammer with a bucking headhaving means for automatically co-planarly aligning the surface of therivet head with the surface of the outer sheet while the hammer is beingused as a bucking tool f during therivet seating operation.

A further object of the invention is to provide a method offlush-riveting of the general character discussed in the foregoing,wherein the head of a rivet is impacted so as to seat the same in nestedrelation to dimpled sheets, and pressure against the rivet head issustained after the impacting theeof and during the upsetting of therivet shank so as to expand the same into circumferential sealingengagement with the edges o'f the sheets forming this perforation and soas to form a head on the rear end of the shank. Some further objects andadvantages will appear in the following part of the specification.

Referring to the drawings which are for illustrative purposes only,

Fig. 1 is a fragmentary sectional view showing how two riveting hammers,embodying a part of our present invention, may be cooperatively employedin the practice of our method of ush-riveting, one being in position forseating the rivet and the other in position for aligning the rivet andbucking the sheets.

Fig. 2 is a fragmentary view showing the driving head, of th'e rivetinghammer used to seat the rivet, fully extended by an impact blow of thehammer piston, and the rivet seated in a dimpled recess in the sheets'asthe result thereof.

Fig. 3 is a fragmentary sectional view illustrating the further steps ofupsetting the rivet strain a piston hammer from forward movement andbuild up a fluid pressure behind the same.

Fig. 8 -is a fragmentary partly sectioned view pressure may be built upprior to the forward movement of the piston hammer I8.

As shown in Figs. 1 and 9, the hammer I5 is provided with a piston grip33 forming part of a metal body 32 which extends downwardly'from thecylinder I6 and has therein an air passage 34 into which air is admittedthrough a spring seated main valve for a suitable air connection 36, thespring 31 of the main valve 35 operating to continuously exert a forceto close the valve. A pivoted trigger 38 is mounted on the handle 33 insuch position that when it is depressed, or, in other words, moved fromits position of Fig. 1 towards its position in Fig. 9, it will engage,9the stem 39 of the' main valve and open the same. The upper end of thetrigger 38 has forks 4I adapted to engage a pin 42 which projectslaterally from an air distributor or transfer valve mechanism 43disposed below and substantially in alignment with the barrel I6.

The transfer valve 43 comprises two cooperating valve members, namely,shuttle valve 45 disposed within the sleeve 44, the pin 42 being securedin the shuttle valve 45 and projecting through longitudinal slots 46 inthe sleeve valve 44. The two valve members 44 and 45 are slidably fittedinto a bore 41 in the metal body 32 of the hammer device I5. Tworecesses 48 and 49 are cut away from the bottom of the shuttle valve 45,and two recesses 50 and 5I are cut away from the top thereof. Inaddition, the shuttle valve 45 is provided with twb annular recesses,'orpassages, 52 and 53. The forward portion of the shuttle valve 45 issmaller in diameter than the rear portion, forming a shoulder 54.

'I'he sleeve valve 44 ts over the forward portion 69, and an openingvthe sleeve valve 44 showing the cooperating parts of thevhammer inposition to release the hammer piston and apply the Whole force of theimpelling fluid to the same during its impacting stroke.

Fig. 9 is a fragmentary partly sectioned view showing the'lcooperatingvalvef-parts inl the respective positions assumed thereby as they returnto initial position, such as illustrated in Fig. 6.

As shown in Fig. 1, ,the embodiment of the in-` vention chosen for thepurpose of illustration comprises a riveting hammer I5 having a cylinderI6 in which a conventionally packed hammer piston I8 is adapted tobereciprocated so as to strike the shank I9 of a selected die or head,held in the socket opening 28 at cylinder I6. The cylinder I6 is closedat its breech by ahead 2| having a stop 22, and the muzzle end of thecylinder is provided with threads 25 to receive a spring 26 adapted tohold theshank I9 in the operative position shown. The fimction of thestop 22 is to provide, as

shown in Figs. 6 and 7, a chamber 28 in which air the front end of theof the shuttle valve 45 and two notches 68 and 18 in the exposed portionof exposes the shuttle. Diametrally aligned ports 1I are formed in thesleeve valve 44.

A Avalve spring latch 18 is sleeve valve 44 from moving with the shuttlevalve 45 during part of the trigger movement. 'I'he free end of thevalve spring latch 18 bears against the shuttle valve 45 either throughnotch 68 or notch 69 in the bottom of the sleeve valve 44.A A frictiondevice of some kind could be lused to retard the movement of the sleevevalve 44, in but the latch is preferred provided to keep the by. theinventors.

The cylinder I6 is provided with front and rear air ports- 55 and 56,connecting the respective ends thereof with the bore 41 in which thedistributar valve 43 is slidable. Ahead of the inlet port 56 there is anopening 51 extending from the cylinder space to the bore 41, in whichopening a pawl 54 is mounted on a transverse pivot 58 so that it:maybev-rotated vertically-to such position that its rear end will engage anannular recess38 in the piston hammer I8, when the same is at the rearend of the cylinder. A spring 59 is provided to rotate the pawl 54 intothe recess and to there hold it until it is disengaged-by the action ofthe shuttle valve 45,`to be hereinafter explained.

'I'he complete cycle of operation of our riveting hammer I5 will now bedescribed. Figs. 1, 6, 7, 8, and 9 show the positions of the piston I8,the pawl 54, the sleeve valve 44, and the shuttle valve 45 at ilvestages during the complete cycle. In Fig. 1 all of the ports are ineffect closed, and the main valve is likewise closed.' When operatingpressure is applied to the trigger 3l it will be iirst moved into theposition in which it is shown a sleeve 44 and a'- position wherein Iforward end of the cylinder in Fig. 6. This moves the pin 42 back in theslots 46, thereby moving the shuttle valve 45 independently of thesleeve valve 44 into the ilrst the annular passage 52 will connect theports 1|, the lower of which ports 1I is in communication through a port80 with the air passage 34. The stem 39 of the valve 35 will be nowdepressed and air will enter the passage 34 and will travel through port80, passage 52` and port 1I to an opening 8| which connects with the farend of an air passage 82 leading to the exhaust port 55. 'This air willenter the I6 and will move the piston I8 rearwardly from the position inwhich it is shown in Fig. y1 to its position of Fig. 6. The piston I8will now be engaged and latched in such rearward position by the pawl54. Air contained in the cylinder I6, behind the piston I8, may pass outthrough the inlet port 56 and through an opening 64 Vin a plug 85- whichis threaded into the rear end of the bore 41.

Movement of the trigger 38 fromits position of Fig. 6 to its position ofFig. '1 moves both the sleeve valve 44 and the shuttle valve 45simultaneously into a new position wherein' the ports 1| and the passage52, respectively, of the sleeve valve 44 and the shuttle valve 45 willbe offset rearwardly from the ports oropenings 80 and 8|, and thepassage 53 in the shuttle valve 45 and a port 86 which connects therightward end of the bore 41 with the rightward end of the air passage34, so that air will pass under pressure from the passage 34 through theannular passage 53 and the inlet port 56 into the space 23, therebypermitting an air pressure to be space and against the rear face of thepiston I8. It will be noted that at this time the piston I8 isrestrained from forward movement by the pawl 54.

Further movement of the trigger 38 simultaneously moves the sleeve valve44 and the shuttle valve 45 from their position of Fig. 1 to theirposition of Fig-8, to bring the annular valve passage 53 of the shuttlevalve 45 into fully open communication with the inlet port 56 and theair port 86, and at the same time bringing a shoulder 90, formed at thefront end of the depression 50, into engagement with the lower end ofthe pawl 54, to rotate such pawl into retracted position thereof, asshown in Fig. 8, and against the yieldable force of the spring 59,thereby releasing the piston I8 so that the air pressure in the rear endof the cylinder I6 may drive the same forwardly at high velocity intoengagement with the inner end of the shank I9.

Upon release, the trigger 38 is moved toward its initial positin by aspring 60. The first return movement of the trigger 38 will betransmitted through the pin 42 to the shuttle valve 45, to move the sameforward in the sleeve valve 44, thereby disaligning the annular passages52 from the ports 1|, as shown in Fig. 9, so that as further forwardmovement of the trigger toward its initial position in Fig. 1, willsimultaneously move the-sleeve valve 44 and the shuttle valve 45 pastthe ports 80 and 8| in disaligned position whereby no air will ybepermitted at this time to pass from the passage 34 into the passage 82.Thereafter the parts of the device will remain substantially in theposition in which they are shown in Fig. 1. the piston I8 willrequiremerely a single rearward movement of the trigger 38 through thepositions described relative to Figs. l, 6, '1, 8, and 9.

built up in this A further single actuation of From the abovedescription of the riveting hammer and its operation, it is apparentthat the piston I8 will travel to the front of the cylinder and strikethe pin I9 at comparatively high velocity, for three reasons. First, thepistonis held atth'e rear of the cylinder I6 long enough to permit thepressure in that portion of the'v cylinder behind the piston to build upto substantially the pressure in the air supply line, so that thepressure against the piston tending to impel the same forwardly will beat a maximum value at the beginning of the stroke. Second, the piston isnot released until the pressure `in the air passage 34 has been built upto substantially the pressure in the supply line 36 and until the inletvalve and the inlet port 56 have been opened to full. extent so thatwhen the piston I8 is finally released a large volume of air at highpressure is provided against the back of the piston throughout itsentire, forward stroke. And third, since the piston I8 is not releaseduntil the exhaust port 55 has been fully opened, as shown in Fig. 8, itis also apparent from the foregoing description of our riveting hammerand its operation, that the loss of air through leakage is reduced to aminimum. Although it is possible to arrange the cooperative transfervalve element so that the piston I8 will be returned to the rear end ofthe cylinder I6 immediately upon release of the trigger 38, we preferthe arrangement shown whereby the piston is returned on the firstrearward movement of the trigger .36, for the reason that when theoperator hears the piston strike the stop 22 he knows that the tool isready for operation before the trigger is pulled all of thevway back toreleased position.

The `driving heads and the bucking head 9| are basically the same. Eachhas a swivelable contacting member resiliently Aheld against a sphericalend portion of a member fastened to the muzzle of the hammer by means ofa spring 26. In the practice of our new riveting method" two of theriveting hammers I5 are employed in opposed relation, as shown in Figs.1, 2, and 3, one being for the purpose of driving or impacting thedriving head 90 against the head of a rivet while the sheets beingriveted are bucked by the bucking head 9| carried by the other of theharnmers, the drive head 90 being then employed to buck the head of therivet during the upsetting of the rivet shank.

The driving head 90 comprises an anvil 92 which is mcunted'on thesemi-spherical forward end 93 of the shank I9 which has a collar 94 toserve both as a stop to keep the stem from being inserted too far intothe muzzle opening 20 and has a shoulder to be engaged by the coilspring 26 which resiliently holds the stem I9 in operative position.'The anvil 92 has a recess 95 which receives the head 93 of the shank I9anda rubber bushing 96 is placed in the recess 95 adjacent the rear faceof the head 93 to hold the parts in engagement and permit a swivelmovement of the head 90 on the shank I9.

' To resist yslippage when in use, the-head 904 is provided with arubber collar If no opposite longitudinal forces are being applied tomove the anvil 92 forward with reference to the collar, ange 99 of thecollar engages the shoulder |00` of the anvil, which shoulder |00defines the forward end of an annular recess |0I in the anvil 92.Therear portion of the collar 91 comprises a rubber spring |02 whichfits into the annular recess I0 I. When the front edge of the rubbercollar 91 is brought into 91 having a shroud' vto ` pendicular to thesheets |30 and |3I.

' parallel to the outer face of the engagement with the work, as in Fig.1, and the anvil 92 is then moved forwardly, the rubber collar 91 will,in eilect, move rearward on the anvil 92 in the mannei` .indicated inFig. 2. At this time there will be an expansion of the rearward portion|02 of the rubber collar 91 owing to the fact that the rear edge |03thereof is restrained from rearward movement by the shoulder |04 at therear end of the annular channel IOI. The friction of rubber on the metalprevents slippage of the head from position. There are a number ofgrooves |05 in the front end of the collar 9'! for passage of air fromthe space between the front face of the anvil 92 and the Work to whichthe device is applied.

The bucking head 9| `includes a bucking anvil IIO having an axialopening III, van annular front face I|2 perpendicular'to the axis of theopening III, and a conical recess I|3 the angle of which corresponds tothe angle of the head I |14 of a ush rivet |I5 with which the buckinghead 9| is to be used. The bucking anvil |I0 has a rearwardly facedsubstantially semi-spherical socket |I6 and a radial iiange IIT. 'Ihesocket I I6 receives the rounded nose ||0 of a tubular tting II9 havingan annular ange |20 disposed adjacent to the iiange |I1. A rubber collarI2I having an internal groove |22 is placed over the adjacent anges and|20, to hold the parts III) and |I9 together, but to permit a limitedswivelling movement of the part |I0 relative to the part II 9. I

The fitting II9 is held against the muzzle of a riveting hammer |5 ofthe same type as the hammer I5, previously described, by means of aspring 26'. The opening |23 of the fitting i||9 has therein an axiallyslidable stem |24, the rear end |25 of which projects throughthe muzzleopening 20 into the front end of the barrel of the riveting hammer I5'so as to be in a position to be Aengaged by the piston I8 of such hammerI5. I'he front end of the stem |24 is provided with a lcylindrical nose|26 adapted to enter the opening of the bucking anvil I|0ivvhen the stemI 24 is driven forwardly by the piston I8 of the riveting hammer I5', asshownin Fig. 3. If the stem is moved forward when the bore I of thebucking anvil I0 is not in axial alignment therewith, the nose I 26,upon entering the bore or opening III, will rotate the anvil IIO intoalignment with the stem |24, owing to the fact that the inner end of thebore I I I is flared so as to direct the nose |26 into the bore I||without damaging the stem |24 or the bucking anvil I0.

In Figs. 1, 2, and 3 sheets |30 shown, such sheets having aligned andI3I are openings |32 receive the shank |33 of the rivet |I5. This rivetII5 is nrst placed, as shown in Fig.- 1, and the driving head 92 isplaced thereagainst, preferably in centralized relation. The |I0 is thenplaced so that its bore III will receive the rear end of the rivet shank|33, the rivbucking head eting hammer I5 being held substantiallyperthere be some disalignment ci the riveting hammer I5' from trueperpendicular position, the bucking head ||0 will swivel onV the nose 8of the iitting I|9 so that the annular face ||2 of the bucking head I I0will rest tightly against the face of the sheet |30, and the axis of thebore III will then be perpendicular to the sheets |30 and I3 I, and such-bore I|| will hold the shank of the rivet |I5 in this perpendicularrelation, so that the outer face of the rivet head 4 will be sheet |3I.The

should No. 203,946, nied riveting hammer 5 may be then actuated so thatthe piston I8 thereof will strike the stem I9, as shown in Fig. 2',there y driving the head 30 toward the bucking head 9| so as to impactthe head 4 of the rivet |I5 into nested relation to the sheets |30 and|3|,thesheets bending inwardly into lthe depression ||3 of the anvil|I0, the annular portions |35 of the sheets |30 and |3| surrounding theopenings |32, thereby forming depressions, or dimples, in centralizedrelation to the opening, the head I I4 being received in the dimple ofthe sheet |3I, with the fiat, front face of such head II4 ush with theface of the sheet I3I, The upsetting ofthe rivet shank is accomplishedin the following Where the sheets being joined are of a flexiblecharacter, the rivet shank may be upset by iirst moving the nose |26 ofthe stem |24 into a|ivanced position in the bore I, so that such noseApril 29, 1938. Although We have shown and described a simpracticalembodiment of our invention,

` but should scope of the hereto appended claims.

We claim as our invention:

1. In an air hammer of the character described,

scribed, the combination of: a cylinder; a piston movable in ,saidcylinder from the rear to the front end thereof to 'deliver an impact;means for supplying a propulsion fluid to said cylinder to move saidpiston from a position remote from the front end thereof to thefront-end of said cylinden; a latch for holding said piston in aposition spaced from-the rear end of said cylinder so that` a pressureaccumulation chamber is thereby formed between the rear face of saidpiston and the rear end of said cylinder and restraining forwardmovement of said piston so that a fluid pressure. may be built up insaid pressure accumulation chamber; and means for releasing sald latch.

3. In an air hammer of the character described, the combination of: acylinder having a, front port, a rear port, and an air inlet space; apiston in said cylinder; means for connecting said air inlet space to asource of air under pressure: and valve means for controlling thefeeding of air from said air inlet space to said ports, said meanscomprising a valve actuating means and a pair of slldably associatedvalve 'members movable forward by said valve actuating means throughconsecutive stages so as to first connect said air inlet space with saidfront port so as to deliver air through said front port to move saidpiston rearward in said cylinder, then to disconnect said air inletspace from said front port and connect said air inlet space to said rearport to build up a pressure behind said piston, and then tc fullyopen'said air inlet space to said rear port so that the full pressure ofair from said source of air under pressure may propel said pistonforward in said cylinder while said front -port is opened to theexterior, said valve members being then returnable to their initialpositionwithout connecting'said front port to said air inlet space andso as to disconnect said rear port from said inlet space.

4. In an air hammer of the character described, the combination of: acylinder having a front port and a rear port; a hammer piston in saidcylinder; means for connecting the air hammer to a source of uidpressure; and means for controlling the entry of. fluid under pressureto said cylinder, said control means having a front valve constructed soas to first admit fluid through said front port so as' to move saidpiston rearward in said cylinder and to then cut off fluid from saidfront port restraining means to hold said piston in the rearward portionof said cylinder and a rear valve operatively connected to said frontvalve to then introduce iluid through said rear port to build up a fluidpressure behind said piston and to supply a large volume of fluid undersubstantially full pressure of said fluid source through said rear portto said cylinder to impel said piston forcibly to the front end of saidcylinder, said control means having a part to release said restrainingmeans after fluid has been introduced through said rear port, and saidfront valve means having means to open the front end of said cylinder tothe exterior after said piston has been moved to the rear end of saidcylinder.

5. In an air hammer of the character described, the combination of: acylinder having a front porch and a rear port; a hammer piston in saidcylinder; means for connecting the air hammer to a source of fluidpressure; a member movable from an initial position to a final position;and means movable by said member for controlling the entryof fluidunderpressure to said cylinder,

said control means comprising a valuable member constructed so that uponfirst movement of said member it will first admit fluid through saidfront port and at the same time connect said rear port to the exteriorso as to move said piston rearward in said cylinder, then upon furthermovement of said member cut off fluid from said front port and introducefluid through said rear port to build up a fluid pressure behind saidpiston and upon still further movement of said member,

4supply a large volume of fluid under substantially full pressure4 ofsaid fluid source through said rear port to said cylinder to impel saidpiston forcibly to the front end of said cylinder, said valve memberbeing arranged to the front end of said cylinder to the exterior aftersaid piston has been moved to the rear end of said cylinder.

6. In an air hammer of 4the character described, the combination of: acylinder; al piston movable in said cylinder from the rear end thereofto the front end thereof to deliver an impact; a latch engaging saidpiston so as to hold the same in a position retracted from the front endof said cylinder; valve means operable to admit a propulsion fluid intothe space in said cylinder behind said piston; and means operating inconsequence of the operation of said valve means to release said latchafter said propulsion fluid has been admitted to the space behind saidpiston.

7. In an air hammer of the character described, the combination of: acylinder; a piston movable in said cylinder from the rear end thereof tothe front end thereof to deliver an impact; a latch engaging said pistonso as to hold the same in a position retracted from the front end ofsaid cylinder; valve means operable.

to admit a propulsion fluid into the space in said cylinder behind saidpiston; a manually movable member for operating said valve means; andmeans arranged to receive movement in consequence of the movement ofsaid member to operate said valve means, for releasing said latch.

8. In an air hammer of the character described, the combination of: acylinder; a piston movable in said cylinder from the rear end thereof tothe front end thereof to deliver an impact; a latch engaging said pistonso as to hold the same in a position retracted from the front end ofsaid cylinder; valve means operable to admit a propulsion fluid into thespace in said cylinder behind said piston; a movable control memberconnected so as to operate said valve means during a part of itsmovement, said control member having a further movement after theoperation of said valve means; and means arranged to receive movement inconsequence of said further movement of said control member, to releasesaid latch.

9. In an air hammer of the character described, the combination of: acylinder part; a. piston part movable in said cylinder part from therear end thereof to the front end thereof to deliver an impact, one ofsaid parts having a shoulder; a releasable latch member extending fromthe other of said parts into engagement with said shoulder to hold saidpiston in a position near the rear end of said cylinder; a valve todeliver fluid under pressure to the space between said piston and therear end of said cylinder; a member operable to open said valve; andmeans operable by said member to release said latch inember.

10. In an air hammer of the character described, the combination of: acylinder; a piston movable in said cylinder from the rear end thereof tothe front end thereof to deliver an impact; mechanical restraining meansengaging said piston and said cylinder so as to hold said piston in aposition near the rear end of said cylinder; a valve to deliver uidunder pressure to the rear face of said piston: a member operable toopen said valve; and means operable by said member to releasesaidrestraining means after said valve is initially opened.

l1. In an air hammer of the character described, the combination of acylinder having front port means and rearport means: a hammer pistonmovable in said cylinder; a valve operating member movable from a tlrstposition through a second position to a third position; a. uid pressuresupply; valve means operable by said valve operating member, 4said valvemeans disconnecting said fluid pressure supply from both of said portmeans when said operating 20 member is in said rst position, said valvemeans having front valve parts operable by movement of said operatingmember from the said iirst position to said second position to connectsaid iiuid pressure supply to said front port means whereby fluidpressure will be applied to the front face of said piston. and to cutoff the supply of fluid from said front port means and open said frontport means when said operating member is moved from said second positionto said third position, and said valve means having rear valve partsoperative to connect said iiuid pressure supply to said rear port meanswhen said operating member is moved from said second position to saidthird position so that uid pressure will be applied to the rear face ofthe said piston.

AGNE T. LUNDGREN, .ALLAN B. ROGERS. VLADIMIR H. PAVLECKA.

' CERTIFICATE oF coRRETToN. Patent No. 2,257,267. -september 5o, 19in.

AGNE T. LUNDGREN, ET AL.

It is hereby certified that error appears in the printed specificetionof the above vnumbered patent requiring correction as follows: Page'5,first column; line 70, claim 5,'for the word "porch" read -port; andthatA the said Letters Patent should be read with this correctiontherein that the same-nay-conform to the record o"the case in the PatentOffice.

' Signed and sealed this 11th day of November, A. D. 1914;.

Henry Van Arsdale, (Seal) Acting Corrmiasioner of Patents.

